TEMPERATURE CHANGES, ETC., DURING CANNING OPERATIONS. 33 



(3) Great pressures are developed when the corn is not precooked, owing 

 to the swelling of the starch and to the included air. 



(4) The continued rise in pressure due to the liberation of gases, while 

 shown, is partially masked, for the reason that the temperature at the center 

 of the can did not reach the retort temperature during the processing period. 



(5) The rate of rise in pressure during processing is greater at the higher 

 processing temperatures. 



(6) The maximum pressures are all somewhat below the theoretical and 

 somewhat (except in the case of those not precooked) above that for water 

 alone, in which the pressures "are considerably below the theoretical. 



VACUUM STUDIES. 



The vacuum readings on cans used in the tests sealed at 70° and 80° 

 C. are shown in Table 9. 



Table 9. — Vacuum tests with corn in No. 2 tin cans. 



Temperature (°C). 



Length of 



process 

 (minutes.) 



Barometer readings. 



Vacuum 

 (inches 

 of mer- 

 cury). 



, Sealing. 



Proc- 

 essing. 



After 

 cooling. 



At 

 sealing. 



After 

 cooling. 



70 



f 100 

 \ 116 

 I 121 



| 100 

 \ 116 

 [ 121 



22J 

 25 

 17J 



25 



24$ 



24} 



120 

 110 

 121 



140 

 120 

 120 



30.05 

 29.99 

 30.08 



29.56 

 29.99 

 30.01 



29.99 

 29.86 

 29.92 



29.62 

 30.01 

 30.05 



12 

 94 



80 



91 

 151 





14| 

 13J 



As in tests upon other materials the higher the processing tem- 

 perature the lower the vacuum, owing to the liberation of gases dur- 

 ing processing. Repeated experiments have shown that for the same 

 reason the longer the processing period the smaller the vacuum. All 

 results are below the theoretical figures. 



Vacuum readings with corn in No. 2 cans sealed in lots at various 

 temperatures and processed intermittently for 1-| hours at 100° C. 

 gave the figures shown in Table 10. 



Concussion tests with corn prepared as in these vacuum tests showed 

 that the susceptibility to denting gradually increased with the rise of 

 sealing temperature. The figures obtained are also shown in Table 10. 



Table 10. — Vacuum readings and concussion tests with com in No. 2 tin cans. 



Sealing temperature (°C). 



Vacuum 

 (inches of 

 mercury). 



Fall of 

 weighted 

 can (cm.). 



22 





8.0 



45 to 50 



3 



7.6 

 11 



14.6 

 21.2 



8.9 



55to60 



8.6 



65 to 70 



7.6 



75to80.... 



6.4 



95 to 100 



5.0 







